1. Field of the Invention
The present invention relates to a video encoder and a portable radio terminal device using the video encoder.
2. Description of the Related Art
In the MPEG scheme as a typical compression/encoding technique for motion pictures, encoding as a combination of motion compensation prediction (inter prediction), intra prediction, discrete cosine transform (DCT) and variable-length encoding is performed.
On the other hand, IEEE TRANSACTION ON CIRCUIT AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL. 13, No. 7, 2003, “Overview of the H.264/AVC Video Coding Standard”, Thomas Wiegand. for ITU-T Rec.H.264 ISO/IEC 14496-10 AVC discloses another motion-picture encoding scheme, called H.264/AVC, which improved encoding efficiency more than the MPEG scheme. In H.264/AVC, in motion compensation prediction, a motion vector is searched for using a plurality of reference pictures, and motion compensation is performed using an optimal motion vector acquired by the search. Thomas Wiegand, Heiko Schwarz, Anthony Joch, Faouzi Kossentini, Senior Member, IEEE, and Gary K. Sullivan, Senior Member IEEE, “Rate-Constrained Coder Control and Comparison of Video Coding Standards” IEEE TRANSACTIONS AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL. 13, NO. 7, JULY 2003 discloses rate-distortion optimization (RDO) as a coding mode selection method for selecting a coding mode that employs an optimal combination of a coding distortion rate and the number of coded bits.
In H.264/AVC, since an optimal motion vector can be determined from a plurality of reference pictures, a high coding efficiency is realized. However, the number of times of block matching for searching for an optimal motion vector is increased in proportion to the number of reference pictures. When the number of times of block matching is increased, the number of calculations necessary for motion compensation prediction is increased. Therefore, when a conventional video encoder is installed, in particular, in a device of low CPU power, such as a portable radio terminal device, it disadvantageously imparts a significant load to the CPU.